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Caio A. S. Coelho and Lisa Goddard

1. Introduction The majority of drought-related hazards and the attendant economic losses and mortality risks reside in the tropics ( Dilley et al. 2005 ). Changes in climate variability, including more frequent and damaging extreme events such as drought, is one of many anticipated impacts of climate change. Estimating how climate variability may change in a warmer world, and how that variability intersects with more slowly evolving climate change, is vitally important to climate risk

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Renu Joseph and Ning Zeng

. 1992 ; Minnis et al. 1993 ; Robock and Mao 1995 ; Robock 2000 and references therein; Jones et al. 2003 ; Wigley 2000 ; Free and Angell 2002 ). This cooling is affected by the injection of sulfuric gas into the stratosphere, which combines with water and oxygen to form small optically important particles that get redistributed producing a veil of aerosol that blocks incoming solar radiation to the earth. Further, the aerosols of low-latitude volcanoes cover the tropics fairly quickly and

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Antonietta Capotondi and Michael A. Alexander

numerical grids used by each model are also different. For example, the ocean component of Community Climate System Model, version 3 (CCSM3) is based on the Parallel Ocean Program and uses a bipolar grid with the northern pole displaced over Greenland. Most ocean components have finer meridional grid spacing in the tropics, to resolve the jetlike structure of the equatorial circulation. Physical parameterizations of subgrid-scale processes, such as convection and mixing, also differ among models

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Alfredo Ruiz-Barradas and Sumant Nigam

to play important roles in generating hydroclimate variability over the central United States (e.g., Barlow et al. 2001 ; Ruiz-Barradas and Nigam 2005 ; Wang et al. 2006 ; Schubert et al. 2009 ). Interestingly, the Great Plains also exhibits some connectivity with the Indian Ocean, which may be a reflection of the role that the tropics play in North Pacific interdecadal climate variability (e.g., Deser et al. 2004 ). The structure and sign of SST correlations with spring precipitation over

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Yochanan Kushnir, Richard Seager, Mingfang Ting, Naomi Naik, and Jennifer Nakamura

midlatitude response over North America is enhanced by a stationary wave anomaly caused by the changes in the location of the convective heating centers in the tropics, which forces low (high) pressure in the Gulf of Alaska and ascent (descent) over the American West [a phenomenon known as the Pacific–North American (PNA) pattern; see, e.g., Horel and Wallace (1981) , Wallace and Gutzler (1981) , and Trenberth et al. (1998) ]. Both the zonally symmetric and wavelike response to ENSO thus lead to

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Siegfried Schubert, David Gutzler, Hailan Wang, Aiguo Dai, Tom Delworth, Clara Deser, Kirsten Findell, Rong Fu, Wayne Higgins, Martin Hoerling, Ben Kirtman, Randal Koster, Arun Kumar, David Legler, Dennis Lettenmaier, Bradfield Lyon, Victor Magana, Kingtse Mo, Sumant Nigam, Philip Pegion, Adam Phillips, Roger Pulwarty, David Rind, Alfredo Ruiz-Barradas, Jae Schemm, Richard Seager, Ronald Stewart, Max Suarez, Jozef Syktus, Mingfang Ting, Chunzai Wang, Scott Weaver, and Ning Zeng

or negative trend pattern, both alone, or superimposed on selected combinations of the Pacific and Atlantic patterns. A number of other auxiliary experiments were proposed to isolate further various mechanisms and time scales of variability. Some isolate the role of the tropics, while others attempt to separate the contributions from ENSO and lower-frequency Pacific variability. Another set of experiments were formulated to assess the impact of land–atmosphere feedbacks. These additional

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Philip J. Pegion and Arun Kumar

trend shows a large-scale increase in height in the tropics and midlatitudes. The increase in height is maximized just south of the Aleutian Islands and southern parts of the Pacific Ocean. The Pacific SST pattern ( Fig. 4 , middle panels) has a more robust response, with increased precipitation over most of the equatorial Pacific and a decrease over the Maritime Continent. There is also a decrease in precipitation over the Amazon, extending across the tropical Atlantic Ocean into Africa, and an

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Alfredo Ruiz-Barradas and Sumant Nigam

experiments The above regressions serve as more than targets for the idealized simulations: they are a “poor man’s” recourse to uncovering the model response to idealized SST forcing—at least a primary assessment of it. Clearly, not all of the idealized DGW experiments could be mimicked this way, for instance, the ones where SST forcing is confined in a subregion (like the tropics) of the whole pattern (shown in Figs. 1a–c ). Even so, regression analysis on routinely generated AMIP simulations can

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Kingtse C. Mo, Jae-Kyung E. Schemm, and Soo-Hyun Yoo

dryness over the southern United States and wetness over the Ohio Valley ( Fig. 10a ). The upper-level jet responds to suppressed convection and shifts northward (colored). The jet extends from the North Pacific ( Fig. 10f ) to the Southwest. In the tropics, a couplet of negative anomalies (contoured) straddles the equator over the cold SSTAs in the tropical Pacific. In midlatitudes, there is a Pacific–North American type of wave train with positive height anomalies close to the West Coast and

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Kirsten L. Findell and Thomas L. Delworth

, primarily from the tropics, is able to induce most of the observed weakening of the East Asian summer monsoon observed between 1950 and 2000. The analysis of Vecchi and Soden (2007) and Vecchi et al. (2008) showed significant dependence of the SST trend pattern on the original SST dataset. They show that the cooling along the equator in the eastern Pacific shown in Fig. 1b , derived from Hadley Centre data, is not present in the SST trend pattern derived from the Smith and Reynolds (2004) dataset

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